[llvm-dev] Error Calling eraseFromParent()

[Ahmad Nouralizadeh via llvm-dev]

Hi. Thanks. I changed the code but the problem exists. This is my new code
which is again very simple:
...
bool runOnFunction(Function &F) override {

vector<Instruction *> dels;
dels.clear();

for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
Instruction *I = &*(It++);

if (auto* op = dyn_cast<BinaryOperator>(I)) {
IRBuilder<NoFolder> builder(op);

Value* lhs = op->getOperand(0);
Value* rhs = op->getOperand(1);
Value* mul = builder.CreateMul(lhs, rhs);

for (auto& U : op->uses()) {
  User* user = U.getUser();
  user->setOperand(U.getOperandNo(), mul);
}
//I->eraseFromParent();
dels.push_back(I);
}
}

for (auto &I : dels) {
I->eraseFromParent();
}
...

On Wed, Aug 8, 2018 at 6:16 PM, mayuyu.io <admin at mayuyu.io> wrote:

> Hi:
> As stated in the documentation you shouldn’t modify it while iterating as
> this invalidates the iterator. Try save the pointers to a vector outside
> your loop and perform erasing in a new loop following your current one.
>
> Zhang
>
> 在 2018年8月8日，07:54，Ahmad Nouralizadeh via llvm-dev <llvm-dev at lists.llvm.org>
> 写道：
>
> Thanks Bjorn! But The problem is still there.
>
> On Wed, Aug 8, 2018 at 2:04 AM, Björn Pettersson A <
> bjorn.a.pettersson at ericsson.com> wrote:
>
>> It looks quite dangerous to erase the instruction I inside the loop when
>> iterating over all instructions in the function.
>> I guess it depends on how the range based iterator is implemented if that
>> works or not.
>>
>> I think that you, for example, can change the range based iteration
>>
>>    for (auto &I : instructions(F))
>>
>> into something like this
>>
>>    for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
>>       Instruction *I = &*(It++);
>>       ...
>>     }
>>
>> That will make sure that you step the iterator before modifying the data
>> structure you iterate over.
>>
>> Regards,
>> Björn
>> ________________________________________
>> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Ahmad
>> Nouralizadeh via llvm-dev <llvm-dev at lists.llvm.org>
>> Sent: Tuesday, August 7, 2018 22:26
>> To: paul.robinson at sony.com
>> Cc: llvm-dev at lists.llvm.org
>> Subject: Re: [llvm-dev] Error Calling eraseFromParent()
>>
>> The code is really simple. But I can not the reason for the segmentation
>> fault. I only know that the eraseFromParent() function leads to it. The
>> whole code is:
>> ...
>> bool runOnFunction(Function &F) override {
>>
>> for (auto &I : instructions(F)) {
>>
>> if (auto* op = dyn_cast<BinaryOperator>(&I)) {
>> IRBuilder<> builder(op);
>>
>> Value* lhs = op->getOperand(0);
>> Value* rhs = op->getOperand(1);
>> Value* mul = builder.CreateMul(lhs, rhs);
>>
>> for (auto& U : op->uses()) {
>>   User* user = U.getUser();
>>   user->setOperand(U.getOperandNo(), mul);
>> }
>>
>> I.eraseFromParent();
>>     }
>>
>> }
>> ...
>> And I think that the code worked well with LLVM-3.6.0 that I tested one
>> year ago. Now, I use LLVM-6.0.0.
>> Regards.
>>
>
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>
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